DEFORMATION AND FLUID MIGRATION IN THE SUBDUCTING SLAB: AN ECLOGITE-FACIES DUCTILE SHEAR ZONE

Fluid migration within subduction zones plays a critical role in controlling rock deformation mechanics and modulating seismicity. Although these processes cannot be directly observed, exhumed paleosubduction terranes contain mineral fabrics that reflect the effects of subduction deformation and the passage of fluid. The Monviso Ophiolite sequence in the Western Alps (Italy) hosts eclogite-facie rocks that provide insight to the dominant deformation mechanisms at these conditions. These eclogite rocks are dominantly composed of clinopyroxene and clinozoisite. Using combined electron backscatter diffraction and energy dispersive spectroscopy maps, the deformation mechanisms of these minerals (e.g. dislocation creep, dissolution-reprecipitation creep) and their relationship with passing fluids can be placed into two categories: 1) dislocation creep - lacking fluid migration - or 2) dissolution-reprecipitation - assistance of fluid migration. Characterizing the changes in mineral microstructures and chemical variations suggests that dislocation creep enhanced permeability, facilitating fluid infiltration. This activated dissolution-reprecipitation creep, which became the dominant deformation mechanism in the ductile shear zone. The rheology of subduction zones remains poorly understood, and placing constraints on the chemical-mechanical feedbacks taking place - such as identifying shear zone strengthening and weakening - is crucial. Using EBSD and microtectonics to establish the relationship between deformation and fluid migration, our understanding of subduction dynamics and their implications for seismic hazards can be advanced.